<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="app">
        <button @click="on">点击</button>
        <p v-if="a" id="aaaa">Vue is awesome!</h1>
            <p v-else>Oh no sad</h1>
    </div>
    <script src="https://cdn.jsdelivr.net/npm/vue@2"></script>
    <script>
        var app = new Vue({
            el: '#app',
            data: {
                a: true,
            },
            methods: {
                on() {
                    this.a = !this.a;
                    Vue.nextTick().then(function() {
                        console.log(document.getElementById('aaaa'))
                    })
                }
            }

        })
    </script>
</body>

</html>